/Engine/Source/Runtime/Engine/Classes/Components/SplineMeshComponent.h
Calculates the spline transform, including roll, scale, and offset along the spline at a specified alpha interpolation parameter along the spline : This is mirrored to Lightmass::CalcSliceTransform() and LocalVertexShader.usf. If you update one of these, please update them all!
FTransform CalcSliceTransformAtSplineOffset ( const float Alpha ) const